The prior art discloses a multiplicity of friction parts for frictionally acting devices, such as for example plates for multiplate clutches or multiplate brakes or synchronizing rings for synchronizing devices, in which the friction part has a friction surface in which are provided grooves which form a groove pattern.
For example, EP 1 371 866 A1 describes a plate for a wet-running multiplate clutch with an annular friction surface. The friction surface has an inner delimiting edge and an outer delimiting edge. At least one groove is provided in the friction surface, which groove runs from the inner delimiting edge to the outer delimiting edge. Here, the groove is divided into a first partial section, which runs from the inner delimiting edge to a deflection point between the delimiting edges, and a second partial section, which runs from the deflection point to the outer delimiting edge, with the second partial section being angled with respect to the first partial section by a predetermined angle. During operation, a punctiform pressure increase in the through-flowing coolant, such as for example oil, occurs at said deflection point, as a result of which adjacent plates of the multiplate clutch are pushed apart from one another. This in turn has the result that the multiplate clutch which is placed out of frictional engagement has a reduced drag torque.
U.S. Pat. No. 5,460,255 describes a wet-running friction clutch which comprises one or more friction plates, on the sides of which are provided annular friction surfaces. The friction surfaces are formed by the surface of a friction lining, specifically a paper friction lining. Here, the friction lining is divided into a plurality of friction lining segments which are arranged on or fastened to the friction plates, with grooves remaining between the friction lining segments, which grooves extend from an inner edge of the friction surface to an outer edge of the friction surface. The individual friction lining segments were cut previously from a continuous strip of the friction lining, such that little friction lining waste was generated. In one specific embodiment of the friction plate, use is made exclusively of triangular friction lining segments. Said triangular friction lining segments are arranged such that, in the circumferential direction of the friction surface, a groove which is inclined forward with respect to a radial line always alternates with a groove which is inclined rearward with respect to the radial line.
A further plate-like friction lining for an automatic transmission or the like is known from DE 43 02 773 A1. The friction part described in said document comprises an annular-disk-shaped retaining plate on which is provided an annular friction surface which is delimited by an inner edge at one side and by an outer edge at the other side. A plurality of sets of grooves are provided in the friction surface, which sets of grooves comprise in each case one first groove, which extends from the inner edge to the outer edge, and one second groove, which extends from a point, which is situated between the inner edge and the outer edge, on the first groove to the outer edge. With regard to the predefined rotational direction of the friction part, both grooves are inclined obliquely rearward with respect to the radial line, with the second groove having a more pronounced inclination. The sets of grooves which are designed in this way are intended to lead to a fast removal of the oil film between the friction part and the associated counterpart in the event of the actuation of the clutch, in order to obtain a high coefficient of friction at an early stage.
The above-described prior art is afflicted with various disadvantages. For example, the speed of the oil film removal has room for improvement in order to obtain a complete frictionally engaging action between the friction part and its counterpart as early as possible. Furthermore, the known groove pattern does not ensure satisfactory cooling of the friction lining or of the friction surface by means of the oil flowing through the grooves. Furthermore, the high pressure of the oil may result in the friction lining being damaged, in particular if said friction lining is a paper friction lining which is applied to the friction plate. A further disadvantage of the known friction part is that the so-called drag torque is not reduced to such a significant extent, or eliminated, by the known groove pattern. It should also be mentioned that the installation of the known friction plate into a clutch must be carried out with great care, since the alignment of the grooves must correspond to the rotational direction, and this makes the production of a clutch composed of the known friction plates more difficult.